Synonymous codon usage pattern in glycoprotein gene of rabies virus.

Rabies virus (RABV) is the causative agent of a fatal nervous system ailment. The disease is zoonotic and prevalent in many developing countries. The glycoprotein (G) of RABV is the major antigenic determinant of the virus and plays a pivotal role in its neurovirulence. Various aspects of 'G' protein biology have been explored, but the factors affecting the nucleotide choice and synonymous codon usage have never been reported. In the present study, we have analyzed the relative synonymous codon usage and effective number of codons (Nc) using 132 'G' protein genes of RABV. Corresponding analysis was used to calculate major trends in codon usage. The correlation between base composition and codon usage as well as the plot between Nc and GC3 suggest that mutational pressure is the major factor that influences the codon usage in the G gene of RABV. In addition, factors like aromaticity, aliphatic index and hydropathy have shown slight correlation suggesting that natural selection also contributes to the codon usage variations of the 'G' gene. In conclusion, codon usage bias in 'G' gene of RABV is mainly by mutational pressure and natural selection.